To configure an interface as a DHCP client, the ip address dhcp interface mode command is used. Consider the following example: We have a small network consisting of a router and a DHCP server. We want to configure the interface Gi0/0 on the router as a DHCP client. This is how this is done: R1(config)#int Gi0/0 R1(config-if)#ip address dhcp

DHCP uses UDP as its transport protocol. DHCP messages from a client to a server are sent to the 'DHCP server' port (67), and DHCP messages from a server to a client are sent to the 'DHCP client' port (68). A server with multiple network address (e.g., a multi-homed host) MAY use any of its network addresses in outgoing DHCP messages. Understanding DHCP Relay Agent Operation, Minimum DHCP Relay Agent Configuration, Configuring DHCP Relay Agent, Configuring a DHCP Relay Agent on EX Series Switches, Configuring DHCP Smart Relay (Legacy DHCP Relay), Disabling Automatic Binding of Stray DHCP Requests, Using Layer 2 Unicast Transmission instead of Broadcast for DHCP Packets, Changing the Gateway IP Address (giaddr) Field to the DHCP Ack or DHCP NAck: Typically, the DHCP server finalizes the process with an acknowledgment, or Ack, allowing the client device to start using the address. In rare cases, the server issues a Negative Acknowledgment, or NAck, because it may have decided that the address is not available in the milliseconds that have passed since it offered the address. The default is port 67. The DHCP server transmits responses to the DHCP clients at a port number one greater than the UDP port specified. For example, if the default port 67 is used, the server listens on port 67 for requests and responds to the client on port 68. The DHCP client initiates a broadcast request on UDP port 67. The client cannot use TCP because it does not have an IP address of its own, nor does it know the DHCP server address. The DHCP server is listening for broadcasts on UDP port 67.

To configure an interface as a DHCP client, the ip address dhcp interface mode command is used. Consider the following example: We have a small network consisting of a router and a DHCP server. We want to configure the interface Gi0/0 on the router as a DHCP client. This is how this is done: R1(config)#int Gi0/0 R1(config-if)#ip address dhcp

DHCP Ack or DHCP NAck: Typically, the DHCP server finalizes the process with an acknowledgment, or Ack, allowing the client device to start using the address. In rare cases, the server issues a Negative Acknowledgment, or NAck, because it may have decided that the address is not available in the milliseconds that have passed since it offered the address. The default is port 67. The DHCP server transmits responses to the DHCP clients at a port number one greater than the UDP port specified. For example, if the default port 67 is used, the server listens on port 67 for requests and responds to the client on port 68. The DHCP client initiates a broadcast request on UDP port 67. The client cannot use TCP because it does not have an IP address of its own, nor does it know the DHCP server address. The DHCP server is listening for broadcasts on UDP port 67. The DHCP client is automatically included when you install the TCP/IP protocol, so all you have to do is configure TCP/IP to use DHCP. To do this, bring up the Network Properties dialog box by choosing Network or Network Connections in the Control Panel (depending on which version of Windows the client is running).

There is an option to overrule that, but it is not available for outbound rules. Hence, to allow DHCP client broadcasts, you will have to exclude them from the rule suggested in this answer, assuming this firewall rule is indeed responsible for breaking your DHCP setup. DHCP clients use the remote UDP port 67 for IPv4 and 547 for IPv6.

There is an option to overrule that, but it is not available for outbound rules. Hence, to allow DHCP client broadcasts, you will have to exclude them from the rule suggested in this answer, assuming this firewall rule is indeed responsible for breaking your DHCP setup. DHCP clients use the remote UDP port 67 for IPv4 and 547 for IPv6. DHCP L2 Relay. Unlike DHCP relay, DHCP L2 Relay is used in the situation that the DHCP server and client are in the same VLAN. In DHCP L2 Relay, in addition to normally assigning IP addresses to clients from the DHCP server, the switch can record the location information of the DHCP client using Option 82. All of a sudden the network at my University has frozen and we managed to isolate the problem to massive amounts of UDP packets sent on the DHCP ports. On closer inspection, we found that some of the clients keep spamming the server with DHCP requests although the server seem to respond. Hi, I have a problem with the configuration of port-security. Sometimes some clients can't get IP address from DHCP server I shutdown the interface, clear the portsecurity MAC address and finally change the port of the client but he can't get IP address. After a moment the client can get the IP address this problem is very strange. For example, to configure the eth0 interface as a DHCP client, we would add the following configuration: The system should now request network parameters from the DHCP server when booting. To run the DHCP process manually, you can use the dhclient command. For example, to run the DHCP process on the eth0 interface, use the following command: The Dynamic Host Configuration Protocol is an extension of the Bootstrap Protocol (BOOTP) developed in 1985 that connects simple devices like terminals and workstations that don’t have a hard drive with a boot server. These devices then access your operating system over the server.